Asphalt is commonly used as a paving material for road construction and maintenance. Typically, asphalt, often referred to as “asphalt binder” or “asphalt cement,” is mixed with aggregate to form material used in asphalt paving. Processing and use of this material by paving crews yields asphalt pavement. The asphalt pavement comprises aggregate held within a continuous phase of the asphalt binder by adherence of the asphalt binder to the aggregate.
The strength and durability of the asphalt pavement depends on various factors such as the properties of the materials used, the interaction of the various materials, the mix design, construction practices and the environment and traffic conditions to which the pavement is exposed. To produce a mix that will have good performance during the lifetime of the pavement, it is important to attain proper coating of the aggregate with the asphalt with the optimum asphalt binder film thickness, good adhesion of the asphalt onto the aggregate, and good cohesive strength of the asphalt.
Conventional pavements suffer from various types of distress modes such as permanent deformation. Permanent deformation is a significant problem for asphalt pavement. A road may be about 80 to 100° F. or more warmer in the summer than it is in the winter. At warmer temperatures, asphalt pavement softens and can creep and move creating ridges and ruts, often referred to as “rutting,” under the weight of heavy trucks passing over it or traffic that has temporarily stopped, such as, for example, at a traffic light intersection, since rutting is dependent on both the weight of the vehicle and the time duration of the weight application. To reduce or prevent rutting, polymers or other materials having a relatively higher modulus than the asphalt, or that can produce a higher modulus asphalt binder at warmer temperatures than the asphalt, are often incorporated into conventional asphalt binders. Typical polymers used to modify asphalt binders to reduce or prevent rutting include elastomers, such as, for example, styrene/butadiene/styrene copolymer (SBS), and plastomers, such as, for example, polyethylene, ethylene-vinyl acetate copolymer (EVA), and the like.
Roads consisting of asphalt pavement are typically comprised of three layers. The first layer is a course of granular material or aggregate. The second layer, called the base course, is comprised of asphalt and aggregates. The top course, or the wearing course, is also comprised of asphalt and aggregates on which automobiles and trucks drive. Optionally, a course between the base course and the wearing course, called the binder course, is sometimes used. The base course is the thickest and most expensive layer to pave. The top layer is exposed directly to the traffic and weather conditions and is the layer most subject to distress. When sufficient cracking or rutting has occurred this layer is removed and repaved leaving the base course intact provided that no cracking or rutting has occurred in this layer. If this base course layer can no longer adequately carry the load, it must be replaced at considerable cost in terms of time and money.
Accordingly, it is desirable to provide methods for fabricating a substantially thinner, and thus more economical, pavement layers that still have adequate resistance to fatigue cracking and rutting. In addition, it is desirable to provide methods for fabricating an asphalt paving material that has more aggregate to aggregate contact. It also is desirable to provide methods for fabricating asphalt pavement material with improved low temperature cracking performance. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.